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  • peavey cs800 1/2 not working

    I have an older(mid 80's?) Peavey CS 800 power amp that has only 1 channel working(1/2 of power amp). does anyone know where I can get schematics or at least where I should start looking for the problem?

  • #2
    Peavey is traditionally happy to mail or email schematics:
    http://www.peavey.com/support/contactinfo/

    Be sure to let them know any pertinent serial number and date code info as there have been many revisions of the CS-800.

    Those things are pretty rock-solid. When they do develop a problem it's usually just one or two shorted power transistors rather than the whole bank like in so many other amps, and the damage usually doesn't extend "upstream".

    Be sure to retouch the solders at all the power transistor socket pins - a typical place for cracking.

    Comment


    • #3
      Or parts@peavey.com Yes, there were several versions, so look on the serial number plate and see if it says CS800 series c, or series b or "zener" even.

      If you are not blowing fuses, there is a four pin Molex connector to the power amp module for each channel. Check it out and see if any of the pins on it have spread and lost contact. usually shorted power transistors will pop the fuse.
      Education is what you're left with after you have forgotten what you have learned.

      Comment


      • #4
        cs800 1chan working!

        Originally posted by stan View Post
        I have an older(mid 80's?) Peavey CS 800 power amp that has only 1 channel working(1/2 of power amp). does anyone know where I can get schematics or at least where I should start looking for the problem?
        Hi there,

        The peavey cs 8oo power amplifier you have is it the old type 3u one!
        ie, when you remove the to cover you can see two large heatsink's with 24 o/p tansistors facing upwards, and two large blue 15000uf on the left. If so these amps are easy to service having repaired them before and replacement part's can be pricey. Repair tip you can use the good channel to help fix it and power the board's on lower supply rail of 30v dual rail. if you need more help I'll be gald to help.
        cheers for now amptech.

        Comment


        • #5
          Hi All,

          I also have a CS-800, the 3U version as amptech describes, s/n 5A-02115255 with the same problem - one bad channel. It had been working fine 'til one day we turned it on and the right channel was dead, with the red clipping LED constantly lit.

          I narrowed down the problem to the driver board that piggybacks on the power transistor board. This board has two #s on the foil side, 111779 and 98808039.

          My plan is to start by replacing the five electrolytic caps on this board, but if anyone's got a better idea, or a schematic, I'm all ears.

          Thanks, Russ aka PatPend


          Originally posted by amptech View Post
          Hi there,

          The peavey cs 8oo power amplifier you have is it the old type 3u one!
          ie, when you remove the to cover you can see two large heatsink's with 24 o/p tansistors facing upwards, and two large blue 15000uf on the left. If so these amps are easy to service having repaired them before and replacement part's can be pricey. Repair tip you can use the good channel to help fix it and power the board's on lower supply rail of 30v dual rail. if you need more help I'll be gald to help.
          cheers for now amptech.

          Comment


          • #6
            Well, I'll say the five caps on the board are far less likely to be the problem than all the transistors and diodes. Schematics are given on request from the factory. See the address in post #3 above or the one in post #2. You were reading the whole thread I hope.

            Generally on these old warriors, an output transistor or two goes and it blows fuses. Watch the four wire molex connector to each modlue, the pins eventually loosen. Check the output terminal posts - are they shorted together? Sign of a shorted output protect triac.
            Education is what you're left with after you have forgotten what you have learned.

            Comment


            • #7
              Hi russ,
              Did you compair dc voltage's between channel's at the o/p end? a balancned o/p stage should be below 1 volt! use a 100w bulb to drain the main filter cap's after switch off.
              cheers for now amptech.

              Comment


              • #8
                Peavey graciously provided schematics for the CS-800 series A and B (circa 1977) - these show a single op-amp on the driver board. Unfortunately I have a later series which has two op-amps on the driver board which probably implements the DDT compressor function.

                I pointed this out to Peavey and they emailed back the same two schematics

                Luckily the other channel working so between that and having the schematics FWIW hopefully it won't take tooo long to figure it out.

                Thanks for the help.

                Comment


                • #9
                  I agree with Enzo. It's usually a semiconductor somewhere. When you find the bad device, check the surrounding circuit to see if it took anything else out (bias resistors, driver circuit, etc). It's not uncommon for a fault to damage things "upstream.

                  I likely have the schem you want. Is it a CS800S or X?

                  Comment


                  • #10
                    Originally posted by Dave Curtis, dB AudioTech View Post
                    .. I likely have the schem you want. Is it a CS800S or X?
                    I believe it's a CS-800 Series "C". Here are some pics:

                    The front of the unit:


                    The back panel:


                    The boilerplate:


                    View of the driver board in question mounted on its output board:
                    Last edited by patpend; 07-01-2007, 10:17 PM.

                    Comment


                    • #11
                      Did you swap driver boards to narrow the problem down to the one in question? If so good on ya'.

                      I would start with both driver boards removed and side-by-side on the bench (better mark that bad one). Then using a meter set to "diode test" compare forward & reverse readings on each semiconductor between boards until you (hopefully) find a difference. That goes for the 2 IC's as well - or you could swap just them before removing the driver boards to see if the problem follows.

                      Bear in mind while checking components that Peavey uses a lot of what look like 1/4 watt resistors but are actually capacitors. They are usually the ones with the more greenish-colored bodies.

                      Comment


                      • #12
                        Looks like the 6531 is shorted. Anyone know a good place to buy replacements (i.e places that don't charge $12.00 to ship a $0.23 transistor that weighs 0.2 grams?)

                        Comment


                        • #13
                          Where are you? PV will sell parts direct, and shipping is included in the price as a rule.

                          The MPS6531 is a generic part and should be available from Allied or Mouser. All the PV xstrs cross to generics, mostly old Moto numbers. And those can be had reasonably from Allied.

                          The CS800 S and X models are a lot later. The S has the switching power supply. And the X is one of the "wind tunnel" designs.
                          Education is what you're left with after you have forgotten what you have learned.

                          Comment


                          • #14
                            I got a 6531 for $0.08 from Mouser, with $4.79 shipping. Not bad. Except that after replacing the shorted one, the channel still does not work. I have the correct schematics now, so back to the workbench I go...

                            Comment


                            • #15
                              It's fixed!

                              It's all fixed mates! Bottom line, I ended up having to replace:

                              On the driver board:
                              Q7 MPS6531 (shorted)
                              CR13 & CR19 1N4148 (shorted)
                              R22 47kOhm (open)

                              I also replaced R22 on the other (working) driver board, because it measured 88k!

                              On the triac board:
                              Q1 SAC187 (shorted) - replaced with a MAC224

                              Thanks to everyone for their support. Special shout-out to amptech for all his help. You guys rock!!

                              Best regards,
                              Russ aka patpend

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